1. Field of the Invention
The present invention relates to a monolithic IC for controlling the spindle motor of a small hard disk drive (HDD) unit, i.e. a motor drive control IC (HDD drive IC) to which power for driving the motor and power for a motor controlling circuit are supplied from different terminals.
2. Description of the Prior Art
For an HDD driving IC, it is usual to supply from different connecting terminals on an IC chip power for driving a spindle motor (motor driving power) and power for a control driving circuit (control circuit driving power) for controlling the motor. This is intended to prevent faulty operation of the control circuit due to a large current flowing to the spindle motor.
While the voltage of motor driving power is usually 5 V or 12 V (or 24 V in rare cases), control circuit driving power is usually 5 V. If the motor driving power voltage is set at 5 V, the same as the control circuit driving power voltage, it is necessary, besides taking adequate measures against faulty operation, to generate an interrupt signal to interrupt power supply to the motor and the output stage of the control circuit when the common power source voltage, which is supposed to be 5 V, drops to 4 V or below, and to generate a brake signal to brake the motor when the voltage drops to 2 V or even below, so that every part of the HDD unit can operate normally and smoothly.
If the voltage of motor driving power is set at 12 V and that of control circuit driving power at 5 V, besides the interrupt signal and the brake signal, another interrupt signal to turn off the power supply to the motor and the output stage of the control circuit is generated in response to a drop of the motor driving power voltage to 10 V or below and another brake signal is generated in response to a drop of the control circuit driving power voltage to 3 V or below. These control circuit and motor operate in response to the logical sum of the interrupt signal and brake signal corresponding to the aforementioned power voltage of 5 V or 12 V.
Since the connecting terminal to the motor driving power source and that to the control circuit driving power source are connected in common on an IC chip when the voltage of motor power driving power and that of control circuit driving power are set at said common voltage of 5 V, a source voltage detecting circuit is composed of a circuit operating on 5 V power, connected to these commonly connected terminals.
If the voltage of motor driving power is set at 12 V and that of control circuit driving power, at 5 V, a source voltage detecting circuit is composed of a circuit operating on 12 V power, connected to the motor power connecting terminal, and another source voltage detecting circuit is composed of a circuit operating on 5 V power, connected to the control circuit power connecting terminal, the output of an OR circuit taking the logical sum of the output signals of these two source voltage detecting circuits being used as the source voltage detection output.
The aforementioned source voltage detecting circuit operating on 5 V power outputs a detection signal which takes on an active level in response to a drop of the voltage of the control power source terminal to 4 V or below, and the source voltage detecting circuit operating on 12 V power outputs a detection signal which takes on an active level in response to a drop of the voltage of the motor driving power source terminal to 10 V or below.
If an HDD unit driving IC in which these source voltage detecting circuits, one operating on 5 V power and the other on 12 V, are used in combination is to be used with a single 5 V power source by commonly connecting the control circuit power source connecting terminal and the motor power source connecting terminal, the output of said OR circuit always takes on an active level because detection signals of the active level are constantly supplied from the circuit operating on 12 V power, and the output of the circuit operating on 5 V is not reflected on the output of the OR circuit, inviting faulty operation. In order to use such an HDD unit driving IC with a single 5 V power source, it is necessary, for instance, to cut off the output wiring of the voltage detecting circuit operating on 12 V power. If this is difficult to accomplish, it is necessary to provide a circuit equipped with only a source voltage detecting circuit operating on 5V power. Therefore, two kinds of circuit are required, one for the single 5 V power source and the other for two power sources of 5 V and 12 V, resulting in a correspondingly limited freedom of design.